1. Field of the Invention
This invention relates to a coupling composed of rod members and knuckle members and adapted to be assembled into a three-dimensional framed structure as a roof of, for example, a stadium, a pavilion or an art gallery or as decoration or interior in a variety of exhibition halls.
2. Description of the Related Art
Heretofore, a three-dimensional framed structure of the kind described above is built up by interconnecting pipe-like rod members end to end via ball-like knuckle members.
The conventional structures of the pipe-like rod members and the knuckle members will now be described with reference to FIG. 9 of the accompanying drawings.
Each of the rod members 1 has a body including a hollow pipe of steel or aluminum and a pair of frustoconical sleeves attached to opposite ends of the hollow pipe by welding. At each end of the rod member 1, a connecting bolt is inserted in the associated sleeve from inside, having a shaft projecting outwardly. The shaft of the connecting bolt has an intermediate portion of a polygonal cross section and is rotatable and movable outwardly and inwardly axially of the sleeve via a rotary member which is fitted on the intermediate portion of the projected shaft and which is polygonal in either outside or inside cross section. Specifically, the polygonal rotary member has a central bore having the same cross-sectional shape as that of the intermediate portion of the connecting bolt and also is in the shape of a hexagonal cylinder so as to be turned by a tool such as a spanner. The bolt has a screw portion having such a length that the bolt projects outwardly from the sleeve and then threadedly extends into a screw hole (described below) in the associated knuckle member 2.
When the bolt is retracted axially into the sleeve to the maximum extent, the extent of retraction is limited such as by a stop ring projecting outwardly from the end surface of the rotary member by a slight extent. This is because during assembling, turning of the rotary member for threaded connection with the knuckle member 2 can be performed quickly by the distal end of the bolt is inserted in the screw hole in the knuckle member 2. If the distal end of the bolt was retracted from the end surface of the rotary member into the rod member 1 a distal end of the rod member 1 was pressed, it would have been very difficult to screw the bolt into the screw hole in the knuckle member 2. For joining the rod member 1 with the knuckle member 2, the distal end of the bolt is inserted just in the mouth of one of plural screw holes in the surface of the knuckle member 2, and then the rotary member is turned in the fastening direction to screw the bolt into the screw hole. With continued turning of the rotary member to screw the bolt into the screw hole in the knuckle member 2, the distal end of the rotary member is pressed against a virtually flat peripheral surface about the screw hole so that the rod member 1 and the knuckle member 2 are firmly joined together. Likewise, another rod member 1 is joined with this knuckle member 2 at another screw hole thereof, and so forth. Thus a framed structure is built up progressively into a three-dimensional form.
However, when this conventional three-dimensional framed structure is constructed into a large-scale building, the structure itself weighs so considerably heavy that if any bolt should happen to be left unfastened during assembling, this would be a cause for a serious accident.
To prevent such an accident, one solution has been proposed by which the extent of axial movement of a bolt can be readily observed from outside by eye. Specifically, the rotary member has a radial through-slit extending axially, and the bolt has a pin insertion hole perpendicular to the axis of the shaft, in which hole a pin is fixedly fitted with its distal end projecting into the through-slit. When the rotary member, with the bolt, is turned, the bolt is moved forwardly and backwardly to a predetermined extent in the axial direction with respect to the rotary member. Therefore if the distal end of the bolt is received just in the mouth of the screw hole and then the rotary member is turned in the fastening direction, the bolt is threadedly inserted into the screw hole so that the rod member 1 and the knuckle member 2 can be joined together. At that time, whether the bolt is left unfastened can be recognized by the position of the distal end of the pin, in the through-slit of the rotary member, of the bolt.
With this conventional coupling, although the bolt can be prevented from being left unfastened, rainwater and dust would tend to permeate into the through-slit of the rotary member so that the bolt as well as other parts contiguous thereto would be corroded, thus exerting a potent influence upon the strength of the knuckle member. Also, since the bolt and the rotary member are joined together by a pin-and-slit connection, it is difficult to achieve an adequate degree of strength against the load when the bolt is fastened.
To solve this corrosion problem, a proposal has been made by, for example, Japanese Patent Laid-Open Publication 30742/1985. According to this proposal, in place of the through-slit of the rotary member, a radial threaded through-hole is formed in the rotary member, while an elongated groove is formed in the peripheral surface of the bolt, extending parallel to the axis of the bolt. And a screw pin is screwed into the threaded through-hole in such a manner that the distal end of the screw pin engages in the elongated groove. The elongated groove is deep locally at the bolt head side so that between the maximum position in which the bolt is fully retracted and the intermediate position in which the bolt is threadedly inserted into the screw hole of the knuckle member part of the way, the head of the screw pin projects from the surface of the rotary member and so that upon completion of fastening of the bolt, the head of the screw pin is retracted from the surface of the rotary member.
Therefore, since the head of the screw pin is retracted into the rotary member as the screw pin is screwed into the through-hole upon completion of fastening of the bolt, whether the bolt is left unfastened can be recognized by whether the head of the screw pin projects from the surface of the rotary member. In this prior structure, since there is no channel or path leading from the surface of the rotary member to its interior, rainwater, dust, etc. cannot permeate into the interior of the rotary member so that the bolt as well as other parts contiguous thereto are prevented from corroding.
For assembling the foregoing conventional three-dimensional framed structure, assuming that the positions of two ball-like knuckle members 2, 2 are already fixed, the distance between these two knuckle members 2, 2 is equal to the distance between the end surfaces of the two rotary members mounted at opposite ends of the rod member 1 and cannot be spread out with ease in view of the relationship with other components. Consequently, the entire length of the rod member 1 becomes practically longer by the length of the exposed distal end of each bolt projecting from the end surface of the associated rotary member so that the lengthened rod member 1 cannot be inserted between the two knuckle members 2, 2. If the lengthened rod member 1 is to be forced between the two knuckle members 2, 2, the framed structure must be pressed on its midportion by, for example, a gigantic jack to make the entire structure resiliently yielded until the rod member 1 can be inserted between the thus spread pair of knuckle members 2, 2, which must be performed in a big way. During that time, the surface of the knuckle member 1 would be damaged or the paint thereon would be peeled off as the distal end of the bolt slides on the surface of the knuckle member 2, and when it comes to the worst, the bolt itself would be broken. As a consequence, the framed structure to be built up must be assembled progressively from one end of its span toward the other end; its assembling order must be carefully decided, and such a decision of the assembling order would be restricted markedly.
To this end, another proposal has been made by, for example, Japanese Utility Model Laid-Open Publication 123102/1986. In this prior structure, a pin projecting radially from the bolt is inserted in an axial slit in the rotary member so that a predetermined extent of axial movement of the bolt relative to the rotary member is allowed and, at the same time, the bolt is normally urged, from its rear side by a resilient member, so as to project from the rotary member. For joining the rod member 1 with the knuckle member 7, the distal end of the bolt is axially aligned with a screw hole in the knuckle member 2 with pushing the bolt into the rotary member against the bias of the resilient member, and then the distal end of the bolt is automatically inserted into the screw hole by the biasing force of the resilient member, whereupon it is started screwing the screw pin. Therefore, according to this prior structure, even in the case the distance between the two knuckle members 2, 2 is exactly equal to the length of the body of the rod member 1, it is unnecessary to apply an excessive force on other parts around and it is also possible to create room for deciding the assembling order.
In case of this proposed structure, therefore, since it is not equipped with any means for holding the bolt temporarily when the bolt is pushed into the rotary member against the bias of the resilient member, the distal end of the bolt normally tends to project from the end surface of the rotary member so that the distal end of the bolt rubs the surface of the knuckle member 2 when the distal end of the bolt is positioned in the screw hole of the knuckle member 2, thus abrading or scratching the surface of the knuckle 2 as before. Further, like Japanese Patent Laid-Open Publication 30742/1985 (discussed above), rainwater and dust tend to permeate from the through-slit of the rotary member so that various parts can be corroded and hence a problem as to the strength would arise. And dust or dirt would be attached to the corroded parts, which would be a hindrance to, for example, disassembling.
Namely, in this prior kind of coupling for three-dimensional frame structure, since the bolt is retracted into the rotary member when the rod member is positioned with respect to the knuckle member, easy setting of the rod and knuckle members can be achieved. However, this prior art has been encountered with the problems that the bolt is left not temporarily held, that temporarily holding is unreliable, that the rotary member tends to be removed, and that the operation when fastening the bolt is laborious.
With the foregoing problems in view, an improvement has been proposed by, for example, Japanese Patent Laid-Open Publications 147029/1988 and 102147/1989. This prior structure, whose general concept is similar to that of the previously proposed prior structure, has an additional feature that the rod member 1 has one or two screw elements movable back and forth radially of only the sleeve or of both the sleeve and the rotary member. In use, when the bolt is to be unfastened, the bolt is pushed into the rotary member against the bias of the resilient member, whereupon the screw element or elements are threadedly advanced to temporarily hold the bolt in that position. When the bolt is to be fastened, the distal end of the temporarily held bolt is axially aligned with the screw hole of the knuckle member 2, whereupon the screw element or elements are threadedly retracted so that the distal end of the bolt is automatically inserted into the screw hole under the bias of the resilient member. According to this prior structure, the surface of the knuckle member 2 can be prevented from being rubbed by the distal end of the bolt when the rod member 1 is set between a pair of the knuckle members 2, 2, thus maintaining the value of product.
However, depending upon the pressing force of the screw element or elements, the bolt tends to move in both the sleeve and the rotary member axially thereof so that the distal end of the bolt would happen to project from the end surface of the rotary member. In the case the two screw elements are used on the sleeve and the rotary member, respectively, it is necessary to threadedly retract each screw element to release the bolt from the temporary holding when fastening the bolt with the knuckle member 1, which is laborious and time-consuming. In addition, the rotary member can be removed easily.
Accordingly also in this prior coupling, since a threaded insertion of the bolt depends on a pin-and-groove connection, it is difficult to achieve an adequate degree of strength against the load when fastening the bolt with the knuckle member. More particularly since the rotary member, on which a moment is exerted from the external, has a screw through-hole extending radially, it is inevitable that the strength of the rotary member would be lowered and that the screw members themselves can easily be deformed.